Method of fabricating anisotropic optical interference filter

Abstract

In a method of manufacturing a one-dimensionally varying optical filter, a substrate is coated to form a stack of layers of two or more different types. The coating may, for example, employ sputtering, electron-beam evaporation, or thermal evaporation. During the coating, the time-averaged deposition rate is varied along an optical gradient direction by generating reciprocation between a shadow mask and the substrate in a reciprocation direction that is transverse to the optical gradient direction. In some approaches, the shadow mask is periodic with a mask period defined along the direction of reciprocation, and the generated reciprocation has a stroke equal to or greater than the mask period along the direction of reciprocation. The substrate and the shadow mask may also be rotated together as a unit during the coating. Also disclosed are one-dimensionally varying optical filters, such as linear variable filters, made by such methods.

The invention claimed is: 
     
       1. A method of manufacturing a one-dimensionally varying optical filter, the method comprising:
 providing a shadow mask wafer having a plurality of shadow masks disposed thereon, at least one of the plurality of shadow masks having an opening fraction along a direction of reciprocation that varies along a direction transverse to the direction of reciprocation; 
 coating a substrate through the at least one shadow mask to form a stack of layers of two or more different types; and 
 during the coating, generating reciprocation between the shadow mask wafer and the substrate in the direction of reciprocation. 
 
     
     
       2. The method of  claim 1  further comprising:
 during the coating, rotating the substrate and the shadow mask wafer together as a unit. 
 
     
     
       3. The method of  claim 1  wherein the providing comprises:
 providing the shadow mask wafer having the plurality of shadow masks disposed thereon, wherein the at least one of the plurality of shadow masks having a one-dimensional array of wedge-shaped openings along the direction of reciprocation with each wedge extending from a narrow end to a wide end along the direction transverse to the direction of reciprocation. 
 
     
     
       4. The method of  claim 1  wherein the providing comprises:
 providing the shadow mask wafer having the plurality of shadow masks disposed thereon, wherein the at least one of the plurality of shadow masks having a density of openings along the direction of reciprocation that varies along the direction transverse to the direction of reciprocation. 
 
     
     
       5. The method of  claim 1  wherein the variation of the opening fraction along the direction transverse to the direction of reciprocation is effective to deposit the one-dimensionally varying optical filter as a linear variable filter. 
     
     
       6. The method of  claim 1  wherein the opening fraction of the at least one shadow mask along the direction of reciprocation varies non-linearly along the direction transverse to the direction of reciprocation. 
     
     
       7. The method of  claim 1  wherein the coating comprises one of sputtering, electron-beam evaporation, and thermal evaporation. 
     
     
       8. The method of  claim 1  wherein:
 the providing comprises providing the at least one of the plurality of shadow masks on the shadow mask wafer having a repeating pattern of one or more openings along the direction of reciprocation; and 
 the generated reciprocation has a stroke equal to or greater than the period of the repeating pattern of one or more openings along the direction of reciprocation. 
 
     
     
       9. The method of  claim 1  wherein the operation of generating reciprocation between the shadow mask wafer and the substrate consists of one of:
 reciprocating the shadow mask wafer in the direction of reciprocation while not reciprocating the substrate; and 
 reciprocating the substrate in the direction of reciprocation while not reciprocating the shadow mask wafer. 
 
     
     
       10. A one-dimensionally varying optical filter manufactured by a method as set forth in  claim 1 . 
     
     
       11. A method of manufacturing a one-dimensionally varying optical filter, the method comprising:
 coating a substrate through at least one of a plurality of shadow masks on a shadow mask wafer to form a stack of layers of two or more different types; and 
 during the coating, generating reciprocation between the shadow mask wafer and the substrate wherein the at least one of the plurality of shadow masks has openings configured to, in combination with the generated reciprocation, define a coating duty cycle that varies along a direction transverse to the direction of reciprocation. 
 
     
     
       12. The method of  claim 11  further comprising:
 during the coating, rotating the substrate and the shadow mask wafer together as a unit. 
 
     
     
       13. The method of  claim 11  wherein the at least one of the plurality of shadow masks has a one-dimensional array of wedge-shaped openings along the direction of reciprocation with each wedge extending from a narrow end to a wide end along the direction transverse to the direction of reciprocation. 
     
     
       14. The method of  claim 11  wherein the at least one of the plurality of shadow masks has a density of openings along the direction of reciprocation that varies along the direction transverse to the direction of reciprocation. 
     
     
       15. The method of  claim 11  wherein the openings in combination with the generated reciprocation are configured to define a coating duty cycle variation along the direction transverse to the direction of reciprocation that is effective to deposit the one-dimensionally varying optical filter as a linear variable filter. 
     
     
       16. The method of  claim 11  wherein the coating comprises one of sputtering, electron-beam evaporation, and thermal evaporation. 
     
     
       17. The method of  claim 11  wherein:
 the at least one of the plurality of shadow masks has a repeating pattern of one or more openings along the direction of reciprocation defining a mask period along the direction of reciprocation, and 
 the generated reciprocation has a stroke equal to or greater than the mask period along the direction of reciprocation. 
 
     
     
       18. The method of  claim 11  wherein the operation of generating reciprocation between the shadow mask wafer and the substrate consists of one of:
 reciprocating the shadow mask wafer in the direction of reciprocation while not reciprocating the substrate; and 
 reciprocating the substrate in the direction of reciprocation while not reciprocating the shadow mask wafer. 
 
     
     
       19. A linear variable filter manufactured by a method as set forth in  claim 11 . 
     
     
       20. A method of manufacturing a one-dimensionally varying optical filter, the method comprising:
 coating a substrate to form a stack of layers of two or more different types; and 
 during the coating, varying the time-averaged deposition rate along an optical gradient direction by generating reciprocation between a shadow mask wafer having a plurality of shadow masks disposed thereon and the substrate in a reciprocation direction that is transverse to the optical gradient direction. 
 
     
     
       21. The method of  claim 20  further comprising:
 during the coating, rotating the substrate and the shadow mask wafer together as a unit. 
 
     
     
       22. A method of  claim 21  further comprising rotating the rotating unit of the substrate and the shadow mask wafer about a second axis as a planet in a planetary configuration. 
     
     
       23. The method of  claim 20  wherein the coating comprises one of sputtering, electron-beam evaporation, and thermal evaporation. 
     
     
       24. The method of  claim 20  wherein:
 at least one of the plurality of shadow masks is periodic with a mask period defined along the direction of reciprocation, and 
 the generated reciprocation has a stroke equal to or greater than the mask period along the direction of reciprocation. 
 
     
     
       25. The method of  claim 20  wherein the operation of generating reciprocation between the shadow mask wafer and the substrate consists of one of:
 reciprocating the shadow mask wafer in the direction of reciprocation while not reciprocating the substrate; and 
 reciprocating the substrate in the direction of reciprocation while not reciprocating the shadow mask wafer. 
 
     
     
       26. A method of manufacturing a one-dimensionally varying optical filter, the method comprising:
 providing a shadow mask wafer having a plurality of shadow masks disposed therein, wherein at least one of the plurality of shadow masks having openings; 
 coating a substrate through the at least one shadow mask to form a stack of layers of two or more different types; and 
 during the coating, generating reciprocation between the shadow mask wafer and the substrate in the direction of reciprocation; 
 wherein the duty cycle of the reciprocating is varied during the coating in order to produce a multiplicity of filters having similar profiles but differing wavelength characteristics via a single deposition. 
 
     
     
       27. The method of  claim 26  wherein the openings of the at least one of the plurality of shadow masks do not have an opening fraction along a direction of reciprocation that varies along a direction transverse to the direction of reciprocation.